Tracer valves for copying machines

ABSTRACT

A tracer valve has a stylus that is automatically biased to contact a template, despite changes in curvature of the template. The stylus has or is connected to a pressure-bearing surface. A plurality of nozzles for compressed air are spaced apart in the valve in a circle around the pressure-bearing surface, the air they emit impinging on that surface. There is a similar series of cylinders containing pressure members such as pistons spaced around the same or a different pressure-bearing surface. The interior of each nozzle is connected to an associated cylinder, spaced at a chosen angle from the nozzle. Each nozzle-cylinder combination is connected individually to a source of pressure fluid. The stylus approaches one of the nozzles more closely than others when the valve is operating, closing that nozzle and raising the pressure in it and its associated cylinder. The pressure member in that cylinder accordingly exerts a biasing force on the stylus. If the curvature of the template changes, the stylus approaches another nozzle and the direction of the biasing force correspondingly changes. This invention relates to tracer valves for copying machines, and in particular to tracer valves in which a stylus bears against a relatively moving template. Changes in the direction of relative movement, corresponding to changes in the contour of the template, are transmitted through the tracer valve and certain controls to govern the movement of a workpiece relatively to a machine tool in order to give the workpiece the contour of the template.

United States Patent 7 1191 De Nova TRACER VALVES FOR COPYING M ACHINES RobertoDe Nova, Pavia, Italy Assignee: Duplomatic S.p.A., Busto Arsizio (Varese), Italy Filed: Sept. 3, 1971 Appl. No.: 177,738

Inventor:

Primary Examiner-Henry Klinksiek Assistant Examiner-Richard Gerard AttorneyRichard C. Sughrue et al.

57 ABSTRACT A tracer valve has a stylus that is automatically biased to contact a template, despite changes in curvature of the template. The stylus has or is connected to a pres- Nov. 6 1973 cylinders containing pressure members such as pistons spaced around the same or a different pressure-bearing surface. The interior of each nozzle is connected to an associated cylinder, spaced at a chosen angle from the nozzle. Each nozzle-cylinder combination is connected individually to a source of pressure fluid. The stylus approaches one of the nozzles more closely than others when the valve is operating, closing that nozzle and raising the pressure in it and its associated cylinder. The pressure member in that cylinderaccordingly exerts a-biasing force on the stylus. if the curvature of the template changes, the stylus approaches another nozzle and the direction of the biasing force correspondingly changes.

This invention relates to tracer valves for copying machines, and in particular to tracer valves in which a stylus bears against a relatively moving template. Changes in the direction of relative movement, corresponding to changes in the contour of the template, are transmitted through the tracer valve and certain controls to govern the movement of a workpiece relatively to a machine tool in order to give the workpiece the contour of the template.

18 Claims, 8 Drawing Figures PATENIEDImv 6 ms 3. 770.238 SHEET 1 OF '6 INVENTOR.

ROBERTO DE Nam BY 27A A T roKni-YJ PATENTEDIUY s 1973 SHEET 3 OF 6 PAIENTEUHUY BIHB 3.710.238

SHEET SM 6 r r 1 TRACERVALVES FOR COPYING MACHINES As is well known in the art, the stylus is mounted in the tracer valve'for movement about a universal pivot point, its movements-in a plane being resolved along two intersecting and usually perpendicular axes. Each axis is associated with a spool in the tracer valve-to control the movement in one direction'of a table on which the template andworkpiece are fixed. Thus, generally one component along the X-axis corresponds to longi tudinal movement of the table on a saddle and the second component along the Y-axis corresponds to transverse movement of the saddle along the machine knee.

in some such copying machines there is a third axis perpendicular to the other axes, located to coincide with the axis of the stylus when the stylus is centralised in the valve. Thus reciprocal movement of the stylus in the'valve implies movement along this third axis, the Z-axis. Valves with this feature allow the copying of three-dimensional templates as opposed to the twodimensional templates copied by a valve having only an X-axis and a Y-axis.

in a copying machine having a tracer valve, it is desirable that the direction'of contouring, i.e., of movement of the template relativelyto the stylus, should be reversible, so that the operator may choose whether to work clockwise or anti-clockwise around the template and workpiece, for, in one case, conventional milling, or in the other case, climb milling.

In the past, it was at one time necessary for an operataining a plunger which, under constant fluid pressure, bears on the stylus toimpart to it the required biasing force. The interior of the nozzle communicates with a selector or pilot valve device which controls a motor which, through a flexible shaft and a worm drive, is adapted to rotate the sleeve. (and with it the stylus) in the tracer valve. When the curvature of the template engaged by the stylus changes, the .gap between the nozzle in the sleeve and the-anvil surface'on the stylus changes, and the pressure in the interior of the nozzle changes. It rises if the change in curvature is in one direction and fails if the change in curvature is in the other direction. This change in pressure actuates the pilot valve to set the motor in operation, turning the sleeve in the tracer valve in the required direction until the pressure in the nozzle is restored to its original value. At this point the plunger is again applying the biasing force in the correct direction.

This arrangement has the disadvantage of great complexity since there are numerous special components. It also has a large number of moving parts and hence is liable to the disturbance and breakdown. of complicated mechanisms.

It also has the disadvantage that it is necessary for the stylus to rotate in the tracer valve in order to exert the properfbiasing force. This means that any deviation from rectilinearity in the stylus leads to an error in the machining of the workpiece. r

tor to holdv the tip of the stylus manually in contact with the template to ensure accurate copying. This system had the obvious disadvantage of requiring anoperators presence at all times. More recently, systems have been developed in which a biasing force is automatically imparted to the stylus so that, once in contact with the template, it remains in contact with a constant pressure. The direction of the biasing force has been found by extensive experiment to lie preferably in the range of 120 to 150 to the tangential line at the point where the stylus contacts the template, and in a direction relatively to' the tangent such as to promote the advance of the template relatively to the stylus. A convenient inclination is 135 from the tangent. A biasing force with this inclination may be considered as having a first component directed towards the template along the normal to the tangent at the point of contact to hold the stylus relatively in contact with the template, and a second component of equal magnitude but directed along the tangent. The second component opposes the action of friction. inclinations other than 135 to the tangent may be desirable, depending on the characteristics of the template, but 135 may be regarded as a satisfactory compromise in nearly every case.

One known system for imparting the biasing force is disclosed in US. Pat. No. 2,909,357, inventor Roy Rosebrook'. In this system the stylus is mounted for universal pivoting movement in a sleeve that is rotatable with the stylus about the centered axis of the stylus in the valve. Fluid under constant pressure is supplied through passages in the wall of the valve to a nozzle or opening in the sleeve that is spaced a small distance away from an anvil surface connected to the stylus some distance above the universal pivot point. In one embodiment, the sleeve is formed with a cylinder diametrically opposite the nozzle but at a location still further above the universal pivot point, the cylinder con- 'An object of the invention is to provide a tracer valve having a device for exerting a biasing force'on the stylus which overcomes or mitagates these disadvantages. In particular, it is an object of the invention to provide a device which eliminates the pilot valve and motor and toothed drive of the prior systemdescribed, and which reduces the moving components to a small number of simple and robust components.

A'further object is ,to provide a device which allows accurate machining of the workpiece even if the stylus is not perfectly rectilinear; and more particularly a device which allows' the stylus to be fixed against rotation in the valve.

The invention provides a tracer valve having a body to contact, such device comprising an annular pressure-bearing surface connected to the stylus and spaced away from the pivot point, a series of nozzles located at intervals from each other in a circle spaced away from the pressure-bearing surface, a series of cylinders equal in member to the number of nozzles, each nozzle being individually connected to a cylinder disposed at a chosen angle from that nozzle, a'pressure member being slidable in each cylinder under pressure prevailing in that cylinder and the nozzle connected to it, the pressure member being adapted to bear on the pressure-bearing surface to bias thestylu's in a direction corresponding to the chosen angle, and including means to supply all the nozzles independently of each other with fluid under pressure.

In operation of the device, contact of the stylus with the template causes the stylus to take up a position such that the pressure-bearing surface is eccentrically located relatively to the circle of nozzles. The pressurebearing surface approaches at least one of the nozzles more closely than others, impeding or preventing the escape of fluid through that nozzle. The pressure in that nozzle and the cylinder connected to it rises, and the pressure member exerts force on the pressure-bearing surface to bias the stylus. When the curvature of the template changes, the stylus moves away from the first nozzle and approaches another. The fluid in the first nozzle now escapes more easily and the pressure exerted by the pressure member in its associated cylinder drops. The nozzle approached by the stylus is fully or partially closed, and its associated cylinder and pressure member now come into operation.

Various embodiments of the invention are described below with reference to the accompanying drawings, in which:. I

FIG.. 1 is a diagrammatic view of a tracer valve of the invention in operation, illustrating the principle of the invention;

FIG. 2 is a diagrammatic view of the valve of FIG. 1, illustrating further aspects of the principle of the invention;

FIG. 3 is a sectional elevation view of the upper portion of a tracer valve of the invention showing one form of device for biasing the stylus;

FIG. 4 is a plan view of the valve of FIG. 3, partly broken away to show interior construction;

FIG. 5 is a sectional elevation view of the upper portion of a tracer valve showing a modified form of biasing device;

FIG. 6 is a simplified perspective view of the distributor of the device of FIG. 5;

FIG. 7 is a diagrammatic view of the connections between nozzles and cylinders in a reversible biasing deviceof a tracer valve of the invention, showing the conditions necessary for clockwise contouring; and

FIG. 8 is a view similar to FIG. 7, showing the condition necessary for anti-clockwise contouring.

In FIG. 1, a tracer valve of a copying machine is generally indicated by the numeral 10. It has a body 12 within which a stylus 14 is mounted for movement about a universal pivot point in the form of a ball 16 secured in a suitableseat. The body 12 accommodates two spools 20 and 22 which are arranged at right angles to each other and are movable in cylinders not shown to resolve movement of the stylus about its pivot into two perpendicular components. The spool 20 corresponds to an X-axis and the spool 22 to a Y-axis. Movement of the spools is transmitted, by means not shown but known in the art, -to devices which drive a table 24 on which are fixed a template 26 and a workpiece 28. to which the contour of the template is imparted by a milling tool 30 mounted and driven by means not illustrated. The valve is arranged with the stylus 14 vertical and carrying at its lower tip a feeler 32 which, in the finishing cut where great accuracy is required; is of the same diameter as the milling tool 30. The table 24 slides on a saddle 34 in a direction parallel to the X- axis, the saddle 34 itself sliding on a machine knee 36 in a direction parallel to the Y-axis. Movement of the table and saddle, is determined by the movement of the spools 20 and 22 in response to movement of the stylus 14 and feeler 32 relatively to the template 26.

Copying machines incorporating a tracer valve with the features generally described so far are known in the art.

The invention provides a device forbiasing the stylus l4 appropriately towards the template 26 so that once it makes contact with the template it retains the contact despite changes in position as the stylus follows the contour of the template around its full periphery. In FIG. 2 the feeler 32 may be' regarded as being viewed in plan so that its circular circumference is seen contacting the template 26 at a point where there is a mutual tangent 34 to feeler and template. The normal to the tangent 34 at the point of contact is indicated by the numeral 36. If the template is moving relatively to the stylus in the direction shown by the arrow 38, the biasing force 40 should be directed to an angle d measured anticlockwise from the tangent 34, as viewed in FIG. 2, the angle 4: being in the range to 150 and preferably If the, direction of movement of the template were the opposite of that shown by the arrow 38, the'biasing force would need to change direction symmetrically with respect to the normal 36.

As seen in FIGS. 1 and 2, the biasing device comprises a pressure-bearing surface in the form of a drum 42 fast with the upper end of the stylus l4 and coaxial withthe stylus. The drum 42 is loosely surrounded by a ring 44 that is' fixed inor forms part of the body 12 of the valve. In an upper plane A-A to which the axis of the ring 44 is normal there is provided a series of nozzles 46 that extend radially with respect to the ring. The nozzles take the form of narrow passages bored in the material of the ring. There are at least three nozzles and preferably a number in the range six to 12. As seen in FIG. 2, each nozzle 46 is connected by a conduit to a cylinder 48 located in a lower plane B-B parallel to the plane A-A, such cylinder being angularly spaced away from its nozzle by 135. Each cylinder has slidable in it a pressure member such as a piston 50 or a ball or the like. The diameter of the cylinder is far greater than that of its associated nozzle. Each nozzle-cylinder combination is connected through a restriction orifice 52 to a supply line 54 of a fluid pressure, preferably compressed air. The restrictors 52 ensure that each nozzlecylinder combination is supplied with fluid independently of the other such combinations. The network of fluid conduits is shown only fragmentarily in FIG. 2, but the general pattern will be discerned.

The stylus 14 is held against rotation about its axis by a pin 18 extending from the body of the valve into a cavity in the ball 16, without interfering with universal pivoting movement of the stylus.

As will be clear from FIGS. 1 and 2, when the feeler 32 contacts the template 26 and the valve is in operation, the drum 42 is moved to an eccentric position in the ring 44 and more particularly to a position in which, in the plane A-A, it closely approaches the nozzle 460 (FIG. 2). Before such approach, air had escaped without special impediment from the nozzle 46a, but after the approach the nozzle 46a is closed or virtually closed by the surface of the drum 42, and the pressure in the nozzle 46a rises. Because of the action of the restrictor 52a, the nozzle-cylinder combination 46a 48a remains isolated for practical purposes from the rethe nozzles is small compared to that of the cylinders,

the effectof the force exerted on the drum by the air at the mouth of the nozzle 46a is negligible.

In practice it has been found that, with a clearance of the order of 0.05 mm. between the drum 42and the ring 44, and eight to 12 nozzles arranged around a ring of a diameter of about 2 cm.,' the effect of all nozzles except that most closely approached by the drum may be ignored; they play. no significant part in generating the biasing force.

Naturally, with change in the contour ofv the template, the point of contact of the template and feeler will change, and the drum 42 will correspondingly change position in the ring 44, leading to the required change in direction of the biasing force 40.

When the valve is supplied with air'through the line 54 but the feeler 32 is not in contact with the template, there can be no reaction force transmitted up the stylus from the template and there isno stability in the position of the drum 42, which precessesin the ring 44 under the action of the successive pistons 50 which act on it. The stylus precesses correspondingly.

FIGS. 3 and 4 show the upper part of a tracer valve 100 incorporating one form of the biasing device. Mounted in a body 102 of the valve is a stylus 104 of which only the upper tip is seen. Fixed in an axial bore of the body is a housing 106 which accommodates a ring 108 havinga cylindrical lower portion 110 which is bored radially to provide 12 cylinders 112 that lie in -a plane. Each cylinder carries a pressure member in the form of a ball 114 that bears on a lower cylindrical part 116 of a composite pressure-bearing member 118 fitted to the stylus 104 to surround it co-axially. The ring 108 also has an upper tapered part 120 in which are formed "'12 nozzles 122 in the form of narrow radial passages. The nozzles are juxtaposed to a portion 124 of the member 118 that 'is tapered at the same angle as the part 120. An O-ring 126 seals the ring 108 in the housing 106, in which it is a hermetic fit in any case, and a circlip 128 holds the ring and housing firmly together.

The housing 106 is surrounded by a large ring 130 156 in the member '118, to allow the member 118 to be raised or lowered on the stylus 104 and thus to vary the clearance between the tapered portion 124 of the member 118 and the tapered part 120 of the ring 108. Such variation alters the speed of the machining operation since it determines the maximum displacement of the spools (not shown) in the valve.

Note that in FIG. 3 the arrangements for the supply of fluid to the nozzle 122 and cylinder 112 seen on the right are omitted for the sake of simplicity.

In use, the screw 154 is adjusted to a suitable value for the machining operation that is to be carried out.

Compressed air is supplied to the inlet 136, and the stylusis brought manually into' contact with the template to allow the operation to begin. When the stylus contacts the template, it moves away from its central position so that the pressure-bearing body 118 atits upper end moves eccentrically in the ring 108. One of the nozzles122 is closely approached by the part 124 of themember 118 and the pressure in that nozzle correspondingly rises to cause its associated cylinder 112,

connected by one of the pipes 144, to undergo an equal pressure rise and force its ball 1 14 towards the cylindrical part 116 of the member 118. The operation is similar to that already described in relation to FIGS. 1 and 2.

FIG. 5 shows a variant which is adapted for reversible machining. A tracer valve 200 has a body 202 in which a stylus 204 is mounted for universal pivotal movement and also for axial movement. The upper tip of the stylus is formed with a spherical head 206 which seats in a sleeve 208 which is fast with the bottom surface of a pressure-bearing plate 210. The plate is tiltable about a universal pivot in the form of a spherical head 212 that seats in a two-part spherical bearing comprising a lower sleeve 214 force-fitted in an axial bore in the plate, and an upper sleeve 216 held in place by a screw 218. The head 212 is fast on a shank 220 that at its upper end is fast with a cap 222. The cap has a skirt that is internally threaded and fits on a complementally threaded quill 224. The quill is slidable in an axial bore in a shaped top member 226 that has an integral axial that is secured to it hermetically by matching shoulders v 131 and a plate 132 that is secured .in place by means not shown. The ring 130 has an internal circumferential groove 134 with an inlet 135 at one point, connected to a source of compressed air that is not shown. The housing 106 is radially bored and tapped at the level of the groove 134 in the region of each nozzle 122 to provide a cavity 136 accommodating a calibrated restrictor in the formof a screw 138 having a longitudinal bore 139. An axial bore 140 intersects each radial bore 136, the bore 140 accommodating a terminal 142 for an external connecting pipe 144. In the plane of the cylinders 112, the housing l06is also provided with radial bores 146 which are outward extensions of the cylinders 106. Each bore 146 houses a terminal 148 for one of the connecting pipes 144. As seenin FIG. 4,

spigot 217. Keys or splines (not shown) prevent rotation of the quill in the top member. A sealing ring 228 is provided between the shank 220 and the quill 224 to prevent the escape of fluid.

The outer periphery of the device is surrounded by a cylindrical shell 230 that has a protective and centering function. I

Loosely surrounding the upper end of the spigot 217 of the top member 226 is an annular plate 232 whose upper surface slides in close contact 'with a flange 234 of the top member 226. The flange 234 has an annular groove 236 which serves as a fluid supply conduit,

being connected to a source of compressed air or other fluid through a radial inlet 238 that is adapted to re- The distributor 242 and spacer 248 rest on a fixed plate 250 on which the distributor is slidable in close contact when the lever 244 is moved. The plate 250 has a series of regularly spaced narrow axial bores forming nozzles 252, and larger bores forming cylinders 254. In practice a preferred number of nozzles is eight or 12; there is an equal number of cylinders. Note that the drawing shows a nozzle in section on the left and a cylinder on the right, whereas in practice with eight or 12 nozzles a true section would show two nozzles or two cylinders located diametrically apart. The nozzles and cylinders are juxtaposed to the top surface of the tilting plate 210 and each cylinder carries a ball 256 as a sliding fit.

The plate 250 is clamped between the spacer 248 at its top and a stepped stem member 258 which extends into' the body 202 of the valve. Screws 260 secure the assembled device to the valve body 202.

Housed in a radial bore in the top member 226 is a stud 262 witha handle 264 at its outer end and an cecentric pin 266 at its inner end. The pin 266 engages in a space between two flanges 268 and 270 on the quill 224. The handle 264 can be turned under friction to cause the pin 266 to raise or lower the quill 224, and with it the shank 220 and the tilting plate 210. This decreases or increases the maximum permissible angle of tilt of the plate 210 in the valve relatively to the fixed plate 250; and so affects the speed of working since it determines the maximum tilting of the stylus 204 from its centered postion in the valve. By making the space between the flanges 268 and 270 somewhat greater than the width of the pin 266, an opportunity is given to the operator to halt the operation rapidly by raising the cap 222 manually to lift the tilting plate into contact with the fixed plate 250 and so prevent it from tiltmg.

As seen in FIGS. and 6,' the plate 232 carries a series of calibrated restrictors 272 equal in number to and arranged at the same intervals as the nozzles 252 in the fixed plate 250. The restrictors 272 are located below the fluid supply groove 236 in the top member 226. Directly below each restrictor 272 is an axial passage 274 for fluid, leading in the position shown in FIG. 5 to a nozzle 252 to supply it with fluid.

In the simplified view of FIG. 6, only one restrictor 272 and axial passage 274 are shown. The drawing also shows a second oblique passage 276 consisting of two rectilinear holes that converge, this passage extending through the annular body of the distributor 242 and emerging at a point on itslower surface located an angle 4) away from the passage 274. The angle 4: is preferably 135. Only small portions of two passages 276 are seen in FIG. 5. In practice there are as many oblique passages 276 as there are restrictors 272 and axial passages 274. Care is taken to prevent interference between these passages when they are drilled in the distributor.

As in the previous embodiments, each nozzle 252 is associated with a cylinder 254 spaced away by an angle o. The passages 274 and 276 serve to keep the pressure in the nozzle and cylinder at the same value. I

In use of the valve, the operator first rotates the cap 222 to set the automatic machining speed at the required value. He then sets the distributor for clockwise or anti-clockwise movement, depending upon the nature of the operation, by moving the lever 244 if necessary from one to the other of its two positions as will be explained more fully in relation to FIGS. 7 and 8. He then starts the machine while manipulating the stylus manually and actuates the rapid traverse knob-264 to bring the template into contact with the stylus. Once this contact is established, he releases the stylus and returns the knob 264 to its zero position. The biasing force applied by the device maintains contact automatically between the template and stylus.

While in contact with the template, the stylus is lo cated off-center in the valve and the plate 210 is accordingly tilted. In any stable condition, i.e., while the stylus engages a zone of constant contour of the template, the plate 210 will remain stable in one position in which it approaches one nozzle 252 more closely than the others andcauses a steep pressure rise in that nozzle and its associated cylinder. The ball 256 of that cylinder will exert the required biasing force on the plate 210 to keep it stably in position. When the stylus encounters a change in the contour of the template, the reaction force transmitted from the template up the stylus to the sleeve 208 and the plate 210 will no longer keep in equilibrium the biasing force of the operative ball 256 and the reaction force of the plate 250 or stem member 258 where contacted by the tilting'plate 2 10.

The plate 210 will accordingly move to another position, tending to re-establish stable conditions. The functioning of the device is thus in principle similar to that of the other embodiments described earlier.

If the operator wishes to reverse the direction of machining, he has merely to move the lever 244 through an angle which, in the case where the biasing angle is ,and where there are 12 nozzles, is 15. This will be clear from the description given below with reference to FIGS. 7 and 8.

FIG. 7 shows an idealized 'ring 300 in the body of a tracer valve. The ring is'formed with 12 nozzles 302 and 12 cylinders 304, each having a piston 306. Each nozzle is connected by a passage 308 shown schematically to'a cylinder displaced 135 from the nozzle in an anti-clockwise direction. The ring loosely surrounds a pressure-bearing surface 310 connecting a stylus rigidly or by an articulated connection. The stylus may be assumed to make contact with a template at a point on the lower end of the stylus axially below the point 312 marked on the circumference of the pressure-bearing member 310. The system is arranged for the stylus to move relatively around the template in clockwise direction.

The passages 308 should be regarded as formed in a distributor 313 that is movable relatively to the ring 300 between two positions in the same fashion as the distributor 242 of FIGS. 5 and 6 is movable relatively to the fixed plate 250 containing the nozzles 252 and cylinders 256. A manually actuatable lever 314 is provided to move the distributor when necessary.

In FIG. 7, the pressure-bearing surface 310 approaches the nozzle 302a more closely than another nozzle, and closes or virtually closes it, bearing against the ring 300. Consequently, the piston 306a in the cylinder 304a that is connected to the nozzle 302a by the passage 308a applies biasing force to the surface 310, biasing the stylus properly towards the template. The

other nozzles and pistons are for practical purposes in- I to the position shown in FIG. 8, the former position of the lever being shown in ghost lines. The pressurebearing member 310 moves diametrically away from the nozzle 302a to the nozzle 3021) and causes the pressure in the nozzle 302b to rise. Pressure in the nozzle 302a falls, and the piston 302a ceases to exert any force on the surface 310. All the passages 308 move anticlockwise through l, and the passage 308a with the cylinder 304a, but now connects a nozzle 302c to a cylinder 304a. n i I I The nozzle 302b is connected to a cylinder 304b by a passage 308b, and because of. the pressure rise in this nozzle, there is a corresponding pressure rise in the cylinder 304b, and'the piston 306b is advanced under force to exert the required biasing force which is inclined at 90 to the force previously exerted for clockwise operation.

It will thus be clear that, with the arrangements of FIGS. 5 and 6, the operator need only displace the distributor through to reverse the direction of working. In all the embodiments described above it will have been noticed that, once the valve is properly adjusted, the only moving parts in the biasing device are the pistons or balls in the cylinders. These are simple and robust components. There is little wear and only a minimal possibility of breakdown. The stylus, being held against rotation, need not be perfectly straight for accurate machining of the workpiece.

Naturally, various modifications are possible within the scope of the invention. For one thing, the valve might havea Z-axis in addition to the other two axes. if the Z-axis coincides with the axis of the stylus in its centered position the bias force generated in the plane defined by the X and Y axes will naturally have no component parallel to the Z-axis, and will not influence movements along the Z-axis.

I claim:

1. A tracer valve having a body, a universal pivot point in said body, a stylus mounted for movement about said universal pivot point, means to resolve the movement of the stylus about said pivot point into two components directed along axes that are inclined to each other, and a device to impart a biasing force to said stylus relatively to a template which it is adapted to contact, said device comprising:

an annularpressure-bearing surface connected to the stylus at a point spaced away from the pivot point for movement in response to stylus deflection;

a series of nozzles located at intervals from each other in a circle with the orifice of each nozzle spaced away from said pressure-bearing surface a distance determined by the deflection of the pressure-bearing surface by the stylus;

a series of cylinders equal in number to the number of nozzles;

' individual connecting means connecting. said each nozzle individuallyto an associated said cylinder disposed at a chosen angle from that nozzle with respect to the center of said circle;

a pressure member slidable in each cylinder under pressure prevailing in that cylinder and in the said nozzle connected to it, and

means to supply all said nozzles independentlyof 0 each other with fluid under pressure, whereby deflection of said stylus varies the said pressure in at least one of said nozzle-cylinder connecting means in accordance with the variation of the spacing of the individual nozzle orifices from said pressure- .bearing surface to thereby move the pressure member associated with said connecting means to bear against said pressure-bearing surface for biasing said stylus in a direction corresponding to said chosen angle.

2. The valve of claim 1, including means to prevent rotation of the stylus about its axis.

3. The device of claim 1, in which thechosen angle is in the range to 150.

4. The valve of claim 3, in whichthe chosen angle is 5 The valve of claim 1, in which there are at least three nozzles.

6. The valve of claim 5, in which the number of nozzles is in the range six to 12. I

7. The valve of claim 1, in which the pressure-bearing surface is fixed on the stylus. v

8. The valve of claim 7 in which the pressure-bearing surface comprises a member separate from thestylus but axially adjustable and lockable on it.

9. The valve of claim 1,'in which the pressure-bearing surface is a member separate from the stylus and movable relatively to it.

10. The valve of claim 9, in which the pressurebearing member is connected to the stylus for movement about a universal pivot point, the pressure members being located in stationary structure in the valve.

11. The valve of claim 10, in which the stylus is movable axially relatively to the pressure-bearing member.

12. The valve of claim 1, including means to move the pressure-bearing surface-relatively to the nozzles in order to vary the permissible movement of the stylus.

13. The valve of claim 1, in which the nozzles lie in av first plane and the cylinders lie in a second plane spaced away from the first plane.

, 14. The valve of claim 1, including a series of passages through each of which a single nozzle is supplied with fluid, each passage having a restrictor in it, the cylinder connected to the nozzle supplied by each passage being connected to the passage downstream of the restrictor.

15. The valve of claim 14, including a single feed line supplying all the passages upstream of the restrictors.

16. The valve of claim 1, including a distributor for fluid, located between the nozzles and the cylinders and being movable between a first position in which the valve is arranged for contouring in one direction and a second position in which it is arranged for contouring in the opposite direction.

17. The valve of claim 16, in which the distributor is an annular member provided with passages passing through it and adapted to register with different nozzles and cylinders in its two positions.

l8. The valve of claim 17, in which in the first position of the distributor, one of a pair of interconnected.

with a cylinder and the second with a nozzle.

t t I l UNITED" STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,770, 238 Dated November 6, 1973 Inventor(s) R b to De Nova 7 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In The Heading;

The Priority Date was omitted. Should read:v

September 4,11970 Italy. 69983-A/70 Signed ar ld sealdthis 2nd day of JuIy' 19 74,

(SEAL) Att'est: EDWARD M. FLETCHER; JR. C.MARSHALLJDA NN' Attesting Off ice'r Commissioner. of Patents- FORM PO-IOSO (10-69) I USCOMM-DC scan-P69 Y u.s. GOVERNMENT Pmi'rms ogrlcz; up (fine-934 

1. A tracer valve having a body, a universal pivot point in said body, a stylus mounted for movement about said universal pivot point, means to resolve the movement of the stylus about said pivot point into two components directed along axes that are inclined to each other, and a device to impart a biasing force to said stylus relatively to a template which it is adapted to contact, said device comprising: an annular pressure-bearing surface connected to the stylus at a point spaced away from the pivot point for movement in response to stylus deflection; a series of nozzles located at intervals from each other in a circle with the orifice of each nozzle spaced away from said pressure-bearing surface a distance determined by the deflection of the pressure-bearing surface by the stylus; a series of cylinders equal in number to the number of nozzles; individual connecting means connecting said each nozzle individually to an associated said cylinder disposed at a chosen angle from that nozzle with respect to the center of said circle; a pressure member slidable in each cylinder under pressure prevailing in that cylinder and in the said nozzle connected to it, and means to supply all said nozzles independently of each other with fluid under pressure, whereby deflection of said stylus varies the said pressure in at least one of said nozzlecylinder connecting means in accordance with the variation of the spacing of the individual nozzle orifices from said pressure-bearing surface to thereby move the pressure member associated with said connecting means to bear against said pressure-bearing surface for biasing said stylus in a direction corresponding to said chosen angle.
 2. The valve of claim 1, including means to prevent rotation of the stylus about its axis.
 3. The device of claim 1, in which the chosen angle is in the range 120* to 150*.
 4. The valve of claim 3, in which the chosen angle is 135*.
 5. The valve of claim 1, in which there are at least three nozzles.
 6. The valve of claim 5, in which the number of nozzles is in the range six to
 12. 7. The valve of claim 1, in which the pressure-bearing surface is fixed on the stylus.
 8. The valve of claim 7 in which the pressure-bearing surface comprises a member separate from the stylus but axially adjustable and lockable on it.
 9. The valve of claim 1, in which the pressure-bearing surface is a member separate from the stylus and movable relatively to it.
 10. The valve of claim 9, in which the pressure-bearing member is connected to the stylus for movement about a universal pivot point, the pressure members being located in stationary structure in the valve.
 11. The valve of claim 10, in which the stylus is movable axially relatively to the pressure-bearing member.
 12. The valve of claim 1, including means to move the pressure-bearing surface relatively to the nozzles in order to vary the permissible movement of the stylus.
 13. The valve of claim 1, in which the nozzles lie in a first plane and the cylinders lie in a second plane spaced away from the first plane.
 14. The valve of claim 1, including a series of passages through each of which a single nozzle is supplied with fluid, each passage having a restrictor in it, the cylinder connected to the nozzle supplied by each passage being connected to the passage downstream of the restrictor.
 15. The valve of claim 14, including a single feed line supplying all the passages upstream of the restrictors.
 16. The valve of claim 1, including a distributor for fluid, located between the nozzles and the cylinders and being movable between a first position in which the valve is arranged for contouring in one direction and a second position in which it is arranged for contouring in the opposite direction.
 17. The valve of claim 16, in which the distributor is an annular member provided with passages passing through it and adapted to register with different nozzles and cylinders in its two positions.
 18. The valve of claim 17, in which in the first position of the distributor, one of a pair of interconnected passages in the distributor registers with a nozzle and the other with a cylinder, and in the second position of the distributor the first passage of that pair registers with a cylinder and the second with a nozzle. 